Pre-menstrual weakness and drowsiness in women are related to a large change in the level of hormones in the body before the onset of menstruation. When there are significant changes in the levels of hormones in the body, such as oestrogen, sex hormones, progesterone, thyroid hormones and norepinephrine, they can directly or indirectly affect the metabolism of substances and energy supply in the body. For example, if thyroid hormone production is low, it can lead to a decrease in the excitability of the central nervous system, resulting in drowsiness and a feeling of dullness.